Selective contacts for crystalline silicon solar cells
[eng] Global energy use has increased, causing a rapid shift in the climate. Renewable energy sources such as solar energy must replace fossil fuels to slow down this trend. In order to achieve this, the amount of power generated by solar energy must increase by a factor of 40 by 2050. As silicon so...
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| Tipo de recurso: | tesis doctoral |
| Estado: | Versión publicada |
| Fecha de publicación: | 2023 |
| País: | España |
| Institución: | Universidad de Barcelona |
| Repositorio: | Dipòsit Digital de la UB |
| OAI Identifier: | oai:diposit.ub.edu:2445/201241 |
| Acceso en línea: | https://hdl.handle.net/2445/201241 http://hdl.handle.net/10803/688863 |
| Access Level: | acceso abierto |
| Palabra clave: | Cèl·lules solars Conductors elèctrics Transport d'electrons Solar cells Electric conductors Electron transport |
| Sumario: | [eng] Global energy use has increased, causing a rapid shift in the climate. Renewable energy sources such as solar energy must replace fossil fuels to slow down this trend. In order to achieve this, the amount of power generated by solar energy must increase by a factor of 40 by 2050. As silicon solar cells account for 90% of the global photovoltaic industry, addressing their existing limiting factors such as efficiency and production cost can help to make a big difference. Therefore, the primary objectives of this thesis are to minimize or replace indium (In) in transparent conducting layers (due to rising In costs) and to develop efficient hole and electron transport layers utilizing more industrial and less expensive ways for silicon heterojunction (SHJ) solar cells. In efficient solar cells, the used transparent conducting oxides must exhibit high mobility and high infrared transparency. Fluorine-doped indium oxide (IFO) films were developed with DC sputtering, achieving a highest mobility of the films of 93 cm2V–1s–1 and an efficiency of 22.6% when used in SHJ solar cells. To reduce the usage of In, stacks containing IFO (with ever decreasing thickness) and transparent conducting aluminum-doped zinc oxide (AZO) on top were prepared, resulting in improved electrical and antireflection properties. In addition, In-free transparent conducting layers were developed using dielectric-metal- dielectric (DMD) structures based on AZO as the dielectric with an ultra-thin silver aluminum metallic interlayer. The optimized DMD structures were used as a front contact for n-type silicon solar cells by introducing a hole-selective vanadium pentoxide (V2O5) dielectric layer. Second, hole transport layers (HTL) for SHJ solar cells were fabricated using the industrially scalable technique of sputtering. Molybdenum oxide (MoOx) films were fabricated either employing reactive sputtering using a metallic target or using conventional sputtering from a ceramic target. Whereas the former led to SHJ solar cells exhibiting a power conversion efficiency (PCE) of 8.8%, the latter allowed for sub-stochiometric MoOx films when using a reducing hydrogen atmosphere and applying temperature to the substrate. Finally, organic dipole interlayers as electron transport layers (ETL) were developed in dopant-free SHJ solar cells. Polyethylenimine (PEI), Poly(amidoamine) (PAMAM) dendrimer, and Deoxyribonucleic Acid (DNA) were the selected organic layers, and the spin coating technique was adopted to fabricate these films. Among the different benefits exhibited by the polymeric layers, three of them must be highlighted: (i) increased interface passivation completely eliminated Fermi level pinning at the metal/semiconductor junction; (ii) the dipole layers demonstrate a significant shift in work function of more than 1 eV in certain cases; (iii) the contact resistance was dramatically decreased, accompanied by an increase of PCE up to 13.8%, 14.5% and 15.5%, when using PEI, PAMAM and DNA as dipole layers, respectively. In sum, high-efficiency SHJ solar cells with high-mobility transparent conductors were achieved, and the electron selective contacts were successfully replaced by organic molecules. Furthermore, the potential to utilize these transparent layers and organic compounds in various electronic devices extends far beyond solar cell applications and should be seen as an attractive trend. |
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